Bismuth is a common active in over-the-counter liquid pharmaceutical formulations. Pharmaceutical formulations containing bismuth are often sold as suspensions (e.g. Pepto-Bismol®, distributed by Procter & Gamble®) and can be used to treat gastrointestinal symptoms including nausea, heartburn, indigestion, upset stomach, and diarrhea.
It can be difficult to formulate bismuth-containing suspensions that are pH stable, physically stable, and have a rheology that is consumer acceptable. Some currently available formulations exhibit an upward pH drift, shortening the product's shelf-life. Other bismuth-containing liquid formulations can suffer from physical instability and can separate into phases, during storage or under freeze-thaw conditions that can be encountered during shipping and handling, which results in an appearance that is unacceptable to consumers. Furthermore, some consumers do not prefer the rheology of current bismuth products, as the product can have non-uniform viscosities, which can result in an uneven, gloppy, pour, making it more difficult to measure the dose and pour without spilling.
However, it is difficult to improve the stability and rheology of bismuth-containing formulations because small formulation changes can significantly impact the formulation's properties and can even exacerbate the stability and/or rheology problems.
As such, there remains a need for a suspension that has improved pH stability, physical stability, and rheology properties.